1. Field of the Invention
The present invention relates to a light guiding apparatus, a lighting apparatus, a space modulation part, and an image projection apparatus.
Priority is claimed on Japanese Patent Application No. 2004-232186, filed Aug. 9, 2004, the content of which is incorporated herein by reference.
2. Description of Related Art
Concurrent with the rapid increase in the luminance level of light emitting diodes (LEDs), lighting apparatuses which employ high luminance LEDs are being used instead of so called lamp lighting apparatuses, which use a conventional halogen lamp or xenon lamp.
Because, compared to conventional lamp light sources, LEDs have a long lifetime, the response time thereof is quick, and the color rendering properties thereof are excellent, the LED is said to be a next-generation light source which has very high utility. Recently, the luminance level of white color LEDs as well as red color, green color, and blue color of LEDs is increasing quickly, and the practical usability of white color LEDs has advanced to the point where conventional white color lighting apparatuses can be replaced by white LEDs.
Furthermore, although there are plans to replace conventional head lamps of vehicles with LED light sources, both a mode which illuminates widely for a short distance and a high beam mode which illuminates to a long distance are needed.
Generally, for the lighting apparatuses, both a use in which such a comparatively wide range of uniform illumination and another use in which a comparatively narrow range of illumination as in a spot light are thought of.
In order to obtain a light of which the spot-lighting ability is high from an LED light source, various examples are proposed in which a wedge shaped light guiding rod (hereinafter called the “taper rod”), which has a function in which an emitted light beam angle is reduced, is applied. (For example, Patent Document 1: Japanese Unexamined Patent Application, First Publication No. H8-234109, and Patent Document 2: Japanese Patent No. 3048353).
The effect of the light beam angle change by the taper rod is determined by the ratio of the light entry area to a light emission area, and in the case in which the light emission area when compared to the light entry area is large, the light beam angle becomes smaller. In a conventional example, in general, a shape of the taper rod in which the allowable light beam angle and the light emission area necessary for the emitted light are satisfied is fixedly determined, and is applied.
On the other hand, an image projection apparatus such as a projector or the like is provided with a display device as a space modulation part in order to modulate the emitted light from the lighting apparatus and generate the projection image. When, for example, such a taper rod is used in the lighting apparatus of the projector, a taper rod is used in which the light beam angle can be made as small as the display device allows.
As such a display device, a display device is proposed in which a plurality of cells which have minute shutter structures are arranged in a matrix shape, and the individual shutters can individually be opened or closed at high speed (for example, Non-Patent Document 1: Fixel Ltd., “Shutter Arrays for Projection Displays”, Israel, June, 2002).
In such a display device, when the emitted light is emitted, control is performed so that the light beam is transmitted through cells in which the shutter is opened, and the light beam is blocked out by cells in which the shutter is closed. Furthermore, the emitted light is modulated by the time ratio of the opening and closing states of the shutters, and a projection image can be generated.
In the case of such a transmission type of display device, the optical components arranged on an optical path from the lighting apparatus to the projection lens can be constituted along a straight line, and a simple constitution and which is suitable for miniaturization can be realized. Moreover, because in the transmission type of display device, polarized light transformation is not involved as in the case of liquid crystals, it is also advantageous in view of light use efficiency.